1. Field of the Invention
The present invention relates to a display device and a terminal unit using the same and more particularly, to a display device capable of displaying different images for a plurality of viewpoints and a terminal unit using the display device.
2. Description of the Related Art
In recent years, mounting Liquid Crystal Display (LCD) devices on small-sized electronic equipment such as projectors and portable telephones has been increasing rapidly to exploit the features of the LCD devices, i.e., low power consumption, reduced weight, and low profile. On the other hand, value-added products to be fabricated by adding some function or performance to the LCD device have also been developed, an example of which is the three-dimensional LCD device capable of displaying three-dimensional images using an optical element that separates images for different viewpoints (i.e., an optical image separation element). With the three-dimensional LCD devices of this type, a viewer can recognize three-dimensional images with the naked eyes without using any dedicated eyeglasses. It is typical that a lens (e.g., a lenticular lens, a fly's-eye lens, or the like) or a parallax barrier is used as the optical image separation element.
For example, an image display device comprising a display panel and a lenticular lens is disclosed in the Patent Document 1 (Japanese Unexamined Patent Publication No. 2004-280052) published in 2004 (see claim 1 and FIGS. 1 and 3). The display panel comprises display pixels arranged in a matrix array, where each of the display pixels is formed by (M×N) sub-pixels for N viewpoints (M and N are natural numbers). The lenticular lens divides the light beams at the respective sub-pixels among the N viewpoints. The (M×N) sub-pixels, which are included in each of the display pixels, are formed in a square region.
With the related-art image display device disclosed in the Patent Document 1, the (M×N) sub-pixels included in each of the display pixels are formed in the square region and therefore, images for the N viewpoints can be generated by these display pixels. If N is two or greater, images for the right eye and those for the left eye can be respectively supplied to the different viewpoints; thus, three-dimensional images can be displayed, where the shape of the display pixel is square. If the same images are displayed by the N sub-pixels, two-dimensional images can be displayed. The resolution of the images at the time two-dimensional images are displayed is equal to that at the time three-dimensional images are displayed. The shape of the display pixel is square at the time two-dimensional images are displayed is equal to that at the time three-dimensional images are displayed.
In this way, the resolution in the event of displaying three-dimensional images and that in the event of displaying two-dimensional images can be equalized to each other and at the same time, a feeling of wrongness does not seen even if three- and two-dimensional images are mixed, and three-dimensional images can be displayed at any positions on two-dimensional images. Moreover, since the shape of the display pixel can be made square, the visibility of images (in particular, characters) is superior (see paragraph 0023).
Another image display device comprising a display panel and a parallax barrier is also disclosed in the Patent Document 1 (see claim 12 and FIG. 21). The display panel comprises display pixels arranged in a matrix array, where each of the display pixels is formed by (M×N) sub-pixels for N viewpoints (M and N are natural numbers). The parallax barrier divides the light beams at the respective sub-pixels among the N viewpoints. The (M×N) sub-pixels, which are included in each of the display pixels, are formed in a square region. This image display device is the same in structure as the above-described related-art image display device except that the parallax barrier is used instead of the lenticular lens. The action and advantages of this image display device are the same as those of the above-described image display device (see paragraphs 0041 and 0042).
A three-dimensional LCD device is disclosed in the Patent Document 2 (Japanese Unexamined Patent Publication No. 7-5417) published in 1995 (see claim 1 and FIGS. 1 to 3). This LCD device displays three-dimensional images using a LCD panel that comprises transparent electrodes formed on the inner surfaces of two substrates in such a way as to be opposite to each other. During the operation, signal voltages are applied across the liquid crystal material confined in the gap between the two substrates of the LCD panel, thereby displaying images. A lenticular lens, which is formed by continuously arranging semi-cylindrical convex lenses along the lateral direction of the LCD panel, is located on the front surface of the display section of the LCD panel. Pairs of stripe-shaped image display regions for the right eye and those for the left eye are formed to extend along the vertical direction of the LCD panel corresponding to the respective convex lenses of the lenticular lens. Stripe-shaped spacers are formed at the respective sections that define the image display regions for the right and left eyes between the upper and lower substrates of the LCD panel.
With the related-art three-dimensional LCD device disclosed in the Patent Document 2, because the pairs of stripe-shaped image display regions for the right eye and those for the left eye are formed corresponding to the respective convex lenses of the lenticular lens, proper three-dimensional images can be displayed. Moreover, because the stripe-shaped spacers are formed at the respective sections that define the image display regions for the right and left eyes between the upper and lower substrates of the LCD panel, the effects applied to the displayed images are made less. At the same time, if the liquid crystal material is injected into the gap between the upper and lower substrates along the longitudinal direction of the stripe-shaped spacers, uneven distribution and move of the spacers do not occur during the injection operation of the liquid crystal material. As a result, a uniform gap between the upper and lower substrates is maintained at all times and proper images are displayed (see paragraphs 0018 and 0030).
Another three-dimensional LCD device is disclosed in the Patent Document 2 (see claim 3 and FIG. 4). Similar to the above-described related-art three-dimensional LCD device of the Patent Document 2, this LCD device displays three-dimensional images using a LCD panel that comprises transparent electrodes formed on the inner surfaces of two substrates in such a way as to be opposite to each other. During the operation, signal voltages are applied across the liquid crystal material confined in the gap between the two substrates of the LCD panel, thereby displaying images. A lenticular lens, which is formed by continuously arranging semi-cylindrical convex lenses along the lateral direction of the LCD panel, is located on the front surface of the display section of the LCD panel. Pairs of stripe-shaped image display regions for the right eye and those for the left eye are formed to extend along the vertical direction of the LCD panel corresponding to the respective convex lenses of the lenticular lens. Stripe-shaped spacers are formed at the respective boundaries where the convex lenses of the lenticular lens are adjacent to each other between the upper and lower substrates of the LCD panel. This LCD device is the same in structure as the above-described LCD device except that the stripe-shaped spacers are formed at the respective boundaries of the convex lenses, not at the respective sections that define the image display regions for the right and left eyes. The action and advantages of this LCD device are the same as those of the above-described related-art LCD device (see paragraphs 0020 and 0038 to 0039).
By the way, with an image display device of the type capable of displaying simultaneously two-dimensional images and three-dimensional images, examples of which are disclosed in the Patent Document 1, to display images for two viewpoints (i.e., N=2), two sub-pixels (i.e., one sub-pixel for the left eye and one sub-pixel for the right eye) are combined together to form a unit pixel. When two different images are generated by using the sub-pixels for the left eye and the sub-pixels for the right eye in consideration of parallax, a three-dimensional image is displayed. When the two same images are generated by using the sub-pixels for the left eye and the sub-pixels for the right eye, a two-dimensional image is displayed. In addition, to display images for three or more viewpoints (i.e., N>3), three or more sub-pixels, the number of which is equal to the number of viewpoints (=N), are combined to form a unit pixel.
When a LCD panel is used as the display panel in the above-described related-art image display devices disclosed in the Patent Document 1, it is required for the LCD panel to have a higher definition than that of an LCD panel designed for ordinary LCD devices incapable of displaying different images for a plurality of viewpoints. This is because if we seek to display images using the same pixel number as that of an LCD panel designed for ordinary LCD devices, the necessary pixel number for the LCD panel will be equal to a multiple (=N) of the viewpoint number. In this way, to conduct sufficient image separation in a high-definition LCD panel, the distance between the pixels formed in the LCD panel and the optical image separation element placed on the front surface (i.e., the surface at the viewer's side) of the LCD panel needs to be reduced as much as possible. For this reason, it is necessary to thin the substrate of the LCD panel placed at the viewer's side.
On the other hand, it is usual for a LCD device to have a small gap between a pair of substrates (i.e., a main substrate and an opposite substrate) to form a space in which a liquid crystal material is confined. To make the gap uniform over the whole surfaces of the pair of substrates, spacers having a predetermined rigidity are arranged between the pair of substrates. It is often that granular or columnar spacers are used for this purpose. For example, many grains are dispersed randomly between the pair of substrates, where the gains are called the “granular spacers”. Alternately, a photosensitive resin may be coated on one of the pair of substrates at the predetermined positions and be exposed and developed by photolithography, thereby forming patterned spacers. These patterned spacers are called the “photolithographic or columnar spacers”. (The reason why the latter spacers are called the “columnar spacers” is that these spacers are arranged at the predetermined positions between the pair of substrates in such a way as to extend across the pair of substrates in the form of column or pillar that support the same.
The granular spacers are dispersed randomly between the pair of substrates and therefore, they may be placed on the pixels. In this case, a disadvantage of large contrast lowering arises because some unevenness of alignment of the liquid crystal molecules occurs in the vicinities of the granular spacers placed on the pixels. Moreover, when the viewer's side substrate of the LCD panel is thinned, there arises another disadvantage that the gap unevenness between the pair of substrates is likely to occur due to the distribution non-uniformity (i.e., randomness) of the granular spacers, and that this gap unevenness is likely to become large gradually due to the rigidity lowering of the substrates and/or the distortion release thereof. Accordingly, it is preferred that the columnar spacers are used for high definition LCD devices.
Furthermore, when the viewer's side substrate of the LCD panel is thinned, a polishing process may be used. Since the granular spacers may be moved within the substrate gap in the polishing process of the viewer's side substrate, there is a possibility that the granular spacers gathered at specific positions are recognized as display unevenness. Accordingly, when a polishing process is used for this purpose, it is essential to use the spacers that will be fixed at the predetermined positions like the columnar spacers.
Because of the above-described reasons, it has been common to use the columnar spacers for high-definition LCD panels.
However, even with a high-definition LCD panel using the columnar spacers, there is a possibility that the regions of the alignment film hidden behind the columnar spacers are not sufficiently rubbed due to the pressing force insufficiency of the rubbing material in the rubbing process of the alignment film for giving the initial alignment to the liquid crystal molecules. This causes a problem that the alignment of the liquid crystal molecules is defective in the regions hidden behind the columnar spacers. Moreover, since the alignment direction of the liquid crystal molecules is distorted near the columnar spacers, a problem that the alignment of the liquid crystal molecules is defective may be arisen even if the rubbing process is not carried out. The defective alignment regions of the liquid crystal molecule, which are formed by the columnar spacers in this way, will give rise to disadvantages (e.g., optical leakage), and as a result, these defective alignment regions will be a cause for various image quality degradations including contrast lowering. To prevent such the image quality degradations, it is sufficient that the defective alignment regions are optically shielded. However, if so, the aperture ratio is lowered significantly. This means that the optical shield of the defective alignment regions is not preferred.
In particular, with a high-definition LCD panel designed for a three-dimensional image display device, the pixels are miniaturized; on the other hand, the columnar spacers need to have such a size as to maintain the substrate gap, in other words, the columnar spacer is unable to be miniaturized on approximately the same level as the pixel. Therefore, the occupation ratio of the columnar spacer in each pixel for a high-definition LCD panel is greater than that for an ordinary (i.e., non-high-definition) LCD panel. As a result, the aperture ratio lowering will appear conspicuously, which means that the necessity for preventing the aperture ratio lowering is very high in a high-definition LCD panel. Accordingly, it is necessary to suppress the image quality degradations caused by the defective alignment regions of the liquid crystal molecule without optically shielding the said defective alignment regions (i.e., without lowering the aperture ratio).
In addition, to maintain the substrate gap uniformly over the whole LCD panel, the columnar spacers are arranged periodically at or in the specific or particular positions in the respective pixels where their heights are the same. Therefore, the aforementioned defective alignment regions caused by the columnar spacers will be formed periodically at or in the specific or particular positions in the respective pixels. For this reason, with a display device capable of displaying different images for a plurality of viewpoints, like a three-dimensional LCD device configured by combining a high-definition LCD panel including the aforementioned columnar spacers with an optical image separation element, there is a disadvantage that the image quality degradations (e.g., optical leakage) due to the aforementioned defective alignment regions will be recognized only at the specific observation positions (in other words, the said image quality degradations will change dependent on the observation positions). Furthermore, since the images for the respective viewpoints are enlarged and displayed, the aforementioned defective alignment regions are likely to be recognized by the viewer.
In particular, when the columnar spacers are arranged at either the sub-pixels for the left eyes or those for the right eyes, the effects of the aforementioned defective alignment regions will appear in the displayed images for the left eyes or those for the right eyes only. Therefore, the image quality difference between the displayed images for the left eyes and those for the right eyes will be conspicuous and very easy to be recognized. Accordingly, it is also necessary to suppress the image quality degradations caused by the periodicity in placement of the aforementioned defective alignment regions.
Because of the above-described reasons, it is strongly desirable for the high-definition LCD panel including the columnar spacers to suppress the effects of the aforementioned defective alignment regions caused by the columnar spacers without lowering the aperture ratio as much as possible.
Each of the related-art three-dimensional LCD devices disclosed in the aforementioned Patent Document 2 comprises the spacers provided between the pair of substrates of the LCD panel, where these spacers correspond to the above-described columnar spacers. These columnar spacers are placed at the respective sections that define the image display regions for the right eyes (which correspond to the sub-pixels for the right eyes) and the image display regions for the left eyes (which correspond to the sub-pixels for the left eyes), or at the respective boundaries where the convex lenses (each of which is equal in width to the unit pixel formed by the combination of the sub-pixel for the left eye and the sub-pixel for the right eye) of the lenticular lens are adjacent to each other. These columnar spacers are stripe-shaped in such a way as to be extended along the sections that define the sub-pixels for the right eyes and those for the left eyes, or along the boundaries where the convex lenses are adjacent to each other.
When the columnar spacers, which are stripe-shaped, are arranged in such a way as to be extended along the sections that define the sub-pixels for the right eye and those for the left eye in a high-definition LCD panel like the columnar spacers of one of the three-dimensional LCD devices disclosed in the aforementioned Patent Document 2, the non-light-transmission portions will be large. This is because the width of the columnar spacers is larger than that of the black matrix defining the sub-pixels for the left eyes and those for the right eyes. Accordingly, the angle where two-dimensional images become unable to be recognized will be large. As a result, there arises a problem that non-light-transmission regions (through which the light does not penetrate due to the existence of the columnar spacers) are generated at the front of the three-dimensional LCD device. This point will be explained concretely with reference to FIG. 1.
In FIG. 1, each of the unit pixels 10 arranged in a matrix array in the LCD panel (not shown) is formed by two sub-pixels adjacent to each other, i.e., a sub-pixel 7 for the right eye and a sub-pixel 6 for the left eye. These unit pixels 10 are arranged close to a lenticular lens 21. The lenticular lens 21 is configured by aligning a plurality of lens elements 21a, each of which is formed by a convex cylindrical lens. Columnar spacers 13, which are extended in the form of stripes perpendicular to the paper face of FIG. 1, are arranged in the respective sections that define the sub-pixels 7 for the right eye and the sub-pixels 6 for the left eye. As shown in FIG. 1, the columnar spacers 13 are larger in width than the sub-pixels 6 and 7 and therefore, the portions through which the light emitted from the light source does not penetrate (i.e., the non-light-transmission portions) will be considerably large according to the width difference between the columnar spacers 13 and the sub-pixels 6 and 7. As a result, the non-light-transmission regions are generated at the front of the three-dimensional LCD device, which causes a problem that the regions where images are not seen are formed.
In the case where the aforementioned stripe-shaped spacers 13 are arranged along the boundaries where the convex lenses 21a (i.e., the unit pixels 10) of the lenticular lens 21 are adjacent to each other, like the other of the related-art three-dimensional LCD devices disclosed in the aforementioned Patent Document 2, if some difference occurs between the pitch of the convex lenses 21a (i.e., the unit pixels 10) and that of the sub-pixels 6 and 7, the boundary lines of the unit pixels 10 and those of the sub-pixels 6 and 7 will deviate from each other in the end portion of the LCD panel. For this reason, as shown in FIG. 2, the columnar spacers 13, which should be placed at the respective boundaries of the sub-pixels 6 and 7, will be placed in such a way as to be overlapped with the sub-pixels 6 or 7 contrary to expectations. As a result, there arises a problem that the non-displayable regions where desired images are unable to be displayed may be formed.
As seen from the aforementioned explanation, problems will arise even if the stripe-shaped columnar spacers 13 are placed in any one of the two forms of the related-art three-dimensional LCD devices disclosed in the aforementioned Patent Document 2 to make a high-definition LCD panel.